WASHINGTON — Breaking a sweat? Researchers are creating a skin patch that can test those droplets while people exercise and beam results to their smartphones, possibly a new way to track health and fitness.

The experimental gadget goes well beyond activity monitors like the Fitbit. A little larger than a quarter, it’s almost like a tiny lab stuck to the skin – and a study published Wednesday found it worked on sweaty bicyclists, sticking even during a long-distance race in Arizona.

If you think of perspiration as just a drippy nuisance, think again.

“Sweat has biochemical components within it that tell us a lot about physiological health,” said John A. Rogers, who directs Northwestern University’s Center for Bio-Integrated Electronics and led the new research.

Today’s wearable technology helps people track their calories, activity and heart rate. A wearable biosensor would be “radically different,” Rogers said.

For simple fitness purposes, it could give an early warning that it’s time to replenish electrolytes before someone starts to feel dehydrated. But with additional research, Rogers envisions more sophisticated use of such devices, such as real-time monitoring of how the body adjusts during military training, or even to screen people for diseases.

Rogers, who did much of the research while at the University of Illinois, has long worked to develop electronic devices that can stretch and twist with the body. The skin-like sweat patch adds the capability of microfluidics: capturing and analyzing body fluid.

How it works: Stick the patch on the skin and start moving. Tiny channels collect perspiration and route it to different compartments where it interacts with chemicals that change color to reflect sweat loss, the perspiration’s acidity level, and concentrations of chloride, glucose and lactate.